1. Field of the Invention
The present invention is directed to an ophthalmic apparatus, and in particular to bifocal eyeglasses for the treatment of patients with low-vision, and more particularly macular degeneration.
2. Description of the Prior Art
The macula is the small center portion of the light sensitive retina, which is the lining at the back of the eye. Light rays from objects come to a focus in the eye on the retina and are converted to electrical impulses that are interpreted by the brain. The macula is responsible for sharp, straight-ahead vision, which is necessary for functions such as reading, driving, and recognizing faces.
Macular degeneration is a disorder that affects the macula causing decreased visual acuity and possible loss of central vision. The degeneration results from a partial breakdown of the retinal pigment epithelium (RPE). Breakdown of the RPE interferes with the metabolism of the retina, causing thinning of the retina [the xe2x80x9cdryxe2x80x9d phase of macular degeneration] and may allow these harmful elements from the blood to damage and scar the retina [the xe2x80x9cwetxe2x80x9d phase of macular degeneration].
This disorder results in the loss of central vision. Peripheral fields are always maintained. Although loss of ability to read and drive may occur from macular degeneration, complete blindness rarely occurs from this disease.
The incidence of macular degeneration increases with each decade over age 50 to almost 15% by the age of 75. There is no known effective prevention. Treatments for macular degeneration include laser photocoagulation, photodynamic therapy. Experimental treatments include surgery, and pharmacologic, radiation, and nutrition therapy.
Patients with macular degeneration should consider ways to maximize their remaining vision so that they can master some daily activities. Optical aids and devices can be recommended by low-vision professionals.
An example of one optical aid that uses peripheral vision to compensate for loss of center vision is the invention described in U.S. Pat. No. 5,088,809 to Portney. Portney uses an intraocular lens, having a converging lens portion and a diverging lens portion, in conjunction with multiple-element spectacles. Thus, to use Portney""s invention, the patient must undergo surgery to implant the intraocular lens, and then wear bully, heavy glasses.
Glasses are also used in another treatment for macular degeneration disclosed in U.S. Pat. No. 4,958,924 to Parker. The Parker invention uses eyeglasses alone, but each lens in the eyeglasses has two lens assembliesxe2x80x94a positive power lens and a negative power lens separated by a fixed airspace. With two lenses separated by an airspace, these glasses are also heavy and bulky.
Thus, it should be apparent that a need exists for an improved ophthalmic device for aiding patients with low-vision or macular degeneration wherein the aid uses a single lens for each eye without the need for an intraocular lens.
To address the above-discussed deficiencies of the prior art, the present invention provides eyeglasses with a single bifocal lens for each eye, where each lens has a distance vision portion and a near vision portion. In each lens, the optical center of the near vision portion is located below a line passing horizontally through the optical center of the distant vision portion, and is located on, the temporal side of a vertical line passing through the optical center of the distance vision portion. The transition between the near portion and the distance portion is preferably smooth.